.TH SETPRIV 1 "July 2014" "util-linux" "User Commands"
.SH NAME
setpriv \- run a program with different Linux privilege settings
.SH SYNOPSIS
.B setpriv
[options]
.I program
.RI [ arguments ]
.SH DESCRIPTION
Sets or queries various Linux privilege settings that are inherited across
.BR execve (2).
.PP
In comparison to
.BR su (1)
and
.BR runuser (1),
.B setpriv
neither uses PAM, nor does it prompt for a password.
It is a simple, non-set-user-ID wrapper around
.BR execve (2),
and can be used to drop privileges in the same way as
.BR setuidgid (8)
from
.BR daemontools ,
.BR chpst (8)
from
.BR runit ,
or similar tools shipped by other service managers.
.SH OPTIONS
.TP
.B \-\-clear\-groups
Clear supplementary groups.
.TP
.BR \-d , " \-\-dump"
Dump the current privilege state.
This option can be specified more than once to show extra,
mostly useless, information.  Incompatible with all other options.
.TP
.B \-\-groups \fIgroup\fR...
Set supplementary groups.  The argument is a comma-separated list of GIDs or names.
.TP
.BR \-\-inh\-caps " (" + | \- ) \fIcap "...  or  " \-\-ambient-caps " (" + | \- ) \fIcap "...  or  " \-\-bounding\-set " (" + | \- ) \fIcap ...
Set the inheritable capabilities, ambient capabilities or the capability bounding set.  See
.BR capabilities (7).
The argument is a comma-separated list of
.BI + cap
and
.BI \- cap
entries, which add or remove an entry respectively. \fIcap\fR can either be a
human-readable name as seen in
.BR capabilities (7)
without the \fIcap_\fR prefix or of the format
.BR cap_N ,
where \fIN\fR is the internal capability index used by Linux.
.B +all
and
.B \-all
can be used to add or remove all caps.
.IP
The set of capabilities starts out as
the current inheritable set for
.BR \-\-inh\-caps ,
the current ambient set for
.B \-\-ambient\-caps
and the current bounding set for
.BR \-\-bounding\-set .
.IP
Note the following restrictions (detailed in
.BR capabilities (7))
regarding modifications to these capability sets:
.RS
.IP * 2
A capability can be added to the inheritable set only if it is
currently present in the bounding set.
.IP *
A capability can be added to the ambient set only if it is currently
present in both the permitted and inheritable sets.
.IP *
Notwithstanding the syntax offered by
.BR setpriv ,
the kernel does not permit capabilities to be added to the bounding set.
.RE
.IP
If you drop a capability from the bounding set without also dropping it from the
inheritable set, you are likely to become confused.  Do not do that.
.TP
.B \-\-keep\-groups
Preserve supplementary groups.  Only useful in conjunction with
.BR \-\-rgid ,
.BR \-\-egid ", or"
.BR \-\-regid .
.TP
.B \-\-init\-groups
Initialize supplementary groups using
.BR initgroups "(3)."
Only useful in conjunction with
.B \-\-ruid
or
.BR \-\-reuid .
.TP
.B \-\-list\-caps
List all known capabilities.  This option must be specified alone.
.TP
.B \-\-no\-new\-privs
Set the
.I no_new_privs
bit.  With this bit set,
.BR execve (2)
will not grant new privileges.
For example, the set-user-ID and set-group-ID bits as well
as file capabilities will be disabled.  (Executing binaries with these bits set
will still work, but they will not gain privileges.  Certain LSMs, especially
AppArmor, may result in failures to execute certain programs.)  This bit is
inherited by child processes and cannot be unset.  See
.BR prctl (2)
and
.I Documentation/\:prctl/\:no_\:new_\:privs.txt
in the Linux kernel source.
.sp
The
.I no_new_privs
bit is supported since Linux 3.5.
.TP
.BI \-\-rgid " gid\fR, " \-\-egid " gid\fR, " \-\-regid " gid"
Set the real, effective, or both GIDs.  The \fIgid\fR argument can be
given as a textual group name.
.sp
For safety, you must specify one of
.BR \-\-clear\-groups ,
.BR \-\-groups ,
.BR \-\-keep\-groups ", or"
.B \-\-init\-groups
if you set any primary
.IR gid .
.TP
.BI \-\-ruid " uid\fR, " \-\-euid " uid\fR, " \-\-reuid " uid"
Set the real, effective, or both UIDs.  The \fIuid\fR argument can be
given as a textual login name.
.sp
Setting a
.I uid
or
.I gid
does not change capabilities, although the exec call at the end might change
capabilities.  This means that, if you are root, you probably want to do
something like:
.sp
.B "        setpriv \-\-reuid=1000 \-\-regid=1000 \-\-inh\-caps=\-all"
.TP
.BR \-\-securebits " (" + | \- ) \fIsecurebit ...
Set or clear securebits.  The argument is a comma-separated list.
The valid securebits are
.IR noroot ,
.IR noroot_locked ,
.IR no_setuid_fixup ,
.IR no_setuid_fixup_locked ,
and
.IR keep_caps_locked .
.I keep_caps
is cleared by
.BR execve (2)
and is therefore not allowed.
.TP
.BR "\-\-pdeathsig keep" | clear | <signal>
Keep, clear or set the parent death signal.  Some LSMs, most notably SELinux and
AppArmor, clear the signal when the process' credentials change.  Using
\fB\-\-pdeathsig keep\fR will restore the parent death signal after changing
credentials to remedy that situation.
.TP
.BI \-\-selinux\-label " label"
Request a particular SELinux transition (using a transition on exec, not
dyntrans).  This will fail and cause
.B setpriv
to abort if SELinux is not in use, and the transition may be ignored or cause
.BR execve (2)
to fail at SELinux's whim.  (In particular, this is unlikely to work in
conjunction with
.IR no_new_privs .)
This is similar to
.BR runcon (1).
.TP
.BI \-\-apparmor\-profile " profile"
Request a particular AppArmor profile (using a transition on exec).  This will
fail and cause
.B setpriv
to abort if AppArmor is not in use, and the transition may be ignored or cause
.BR execve (2)
to fail at AppArmor's whim.
.TP
.B \-\-reset\-env
Clears all the environment variables except TERM; initializes the environment variables HOME, SHELL, USER, LOGNAME
according to the user's passwd entry; sets PATH to \fI/usr/local/bin:/bin:/usr/bin\fR for a regular user and to
\fI/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin\fR for root.
.sp
The environment variable PATH may be different on systems where
.I /bin
and
.I /sbin
are merged into
.IR /usr .
The environment variable SHELL defaults to \fI/bin/sh\fR if none is given in the user's
passwd entry.
.TP
.BR \-V , " \-\-version"
Display version information and exit.
.TP
.BR \-h , " \-\-help"
Display help text and exit.
.SH NOTES
If applying any specified option fails,
.I program
will not be run and
.B setpriv
will return with exit status 127.
.PP
Be careful with this tool \-\- it may have unexpected security consequences.
For example, setting
.I no_new_privs
and then execing a program that is
SELinux\-confined (as this tool would do) may prevent the SELinux
restrictions from taking effect.
.SH EXAMPLES
If you're looking for behaviour similar to
.BR su (1)/ runuser "(1), or " sudo (8)
(without the
.B \-g
option), try something like:
.sp
.B "    setpriv \-\-reuid=1000 \-\-regid=1000 \-\-init\-groups"
.PP
If you want to mimic daemontools'
.BR setuid (8),
try:
.sp
.B "    setpriv \-\-reuid=1000 \-\-regid=1000 \-\-clear\-groups"
.SH AUTHORS
.MT luto@amacapital.net
Andy Lutomirski
.ME
.SH SEE ALSO
.BR runuser (1),
.BR su (1),
.BR prctl (2),
.BR capabilities (7)
.SH AVAILABILITY
The
.B setpriv
command is part of the util-linux package and is available from
.UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .
